The present invention is directed to automatic telephone dialers, particularly dialers of the type used with private-branch-exchange (PBX) systems.
The recent advent in the United States of specialized common carriers (SCCs) that provide long-distance telephone networks has brought with it the development of automatic dialers because use of a specialized common carrier often necessitates the dialing of a large number of digits to gain access to the SCC's network. A common procedure for using a specialized common carrier involves two steps. First the user places a call through the local telephone operating company to the facilities of the SCC. The facilities of the SCC then send a prompting signal to the user to indicate that he should transmit his authorization code, which identifies the user for billing purposes. The user then dials the destination telephone number, and the facilities of the specialized common carrier operate to connect the calling station to the destination station via the SCC's network and the local operating company that services the destination.
This type of operation necessitates the dialing of a large number of digits; the caller must first dial a telephone number to access the specialized common carrier, then an authorization code, and finally a destination telephone number. Automatic dialers relieve the caller of the need to dial so many digits; they automatically dial the local access number of the specialized common carrier as well as the caller's authorization code. The caller then has only to dial the telephone number of the destination station.
Although automatic dialers have in the past included some modest complexity because of the need to recognize different types of dial tones and other prompting signals, their interconnections to other apparatus have been relatively simple; in a PBX system, the interconnections consist of a connection over one line to the PBX and over another line to the local telephone company. Thus, the provision of automatic dialing has not necessitated a wholesale change in the PBX, and the use of dialers has accordingly proved economical in many situations.
However, such dialers cannot be used by subscribers with centrex service, in which PBX-like features are provided without PBX equipment on the subscriber's premises. This is because conventional dialers must be interposed at the junction between the switching equipment and the "outside" line, and this junction is not on the subscriber's premises.
Another limitation of conventional dialers becomes apparent when the subscriber employs dedicated outside lines. Although the specialized-common-carrier subscriber usually obtains access to the SCC's facilities through connections provided by the local telephone operating company, this arrangement necessitates payment not only to the specialized common carrier but also to the local telephone company. Accordingly, it is desirable to have a separate dedicated circuit connected directly to the specialized common carrier. In fact, it may be desirable to employ dedicated lines for more than one specialized common carrier.
For the subscriber to use a conventional dialer to choose among the various outside lines, however, the dialer must be connected not only to several outside lines but also to the same number of PBX lines. The dialer would thus have to include its own complicated switching network; each dialer would have to be a miniature PBX. This requirement would eliminate much of the attractiveness of the dialer.
It is accordingly an object of the present invention to provide automatic dialing to subscribers having dedicated lines to specialized-common-carrier facilities but to omit the complicated switching arrangements that conventional dialers would require.
It is another object of the present invention to provide automatic dialing to subscribers who have centrex service.